Several world-renowned works of art were stolen from the Dutch Kunsthal Museum in Rotterdam. Thieves made away with works by Pablo Picasso, Henri Matisse, Claude Monet, and others, worth up to hundreds of millions of dollars.

The thieves broke into the museum during the early hours of Tuesday morning. It is one of the largest art heists in years. They also got away with works by Lucian Freud, Paul Gauguin, and Meyer de Haan.

The works, which are part of the private Triton Foundation collection, were on public display for the first time as part of the museum's 20th anniversary.

The museum staff are baffled as to how the thieves were able to pull off the heist. However, the security system, which was supposedly functional, is automated and no guards are used on site.

"It's every museum director's worst nightmare," Kunsthal director Emily Ansenk told the Associated Press.

The museum's alarm system did go off and police arrived five minutes later, but they could not find the thieves. Police are now reviewing surveillance footage.

Willem van Hassel, the museum's chairman, said its security systems are automated, and do not use guards on site.

Chris Marinello, who directs the Art Loss Register says the stolen paintings could be worth "hundreds of millions of euros" at auctions, according to the AP. However they would have to be legally sold, which would not be possible since they are regarded as stolen items.

The pieces include Pablo Picasso's 1971 "Harlequin Head"; Claude Monet's 1901 "Waterloo Bridge, London" and "Charing Cross Bridge, London"; Henri Matisse's 1919 "Reading Girl in White and Yellow"; Paul Gauguin's 1898 "Girl in Front of Open Window"; Meyer de Haan's "Self-Portrait," around 1890, and Lucian Freud's 2002 work "Woman with Eyes Closed," according to AP.

While the thieves couldn't legally sell the paintings, they can sell them on the black market, but they likely wouldn't get as much money as they're worth. However, they may also try to ask for ransom money from the painting's owners or the museum.

Despite losing the works, the owners of the Triton Foundation Collections say that they will continue to display the rest of the paintings.

The Kunsthal Museum closed as police led investigations on Tuesday, but it is set to reopen on Wednesday. The museum does not have its own collection and often hosts temporary exhibits.